Roadways made of concrete, asphalt or other materials are subject to extreme conditions caused by weather and traffic which eventually lead to defects in the roadway surface, such as cracks and potholes. While some of these defects can be repaired by using localized patching, there comes a time when a roadway surface has become so degradated that it must be removed and replaced, or otherwise repaired or resurfaced over a large extent.
Many types of construction equipment utilize a mobile chassis with a drum mounted on an underside thereof to perform an operation on worn roadway surfaces and/or road beds. Two of such types of machines are cold planers and reclaimer/stabilizer machines. In such machines, cutting teeth are arranged on the drum in a desired configuration, such as a spiral configuration, to cut the surface and to assist, in the case of a cold planer, in picking up and transferring the removed roadway cuttings to a conveyor which, in turn, conveys the cuttings into a dump truck or other suitable vehicle for transferring the cuttings to a proper disposal or recycling location, which recycling may be at or near the work site.
As is known in the art, cold planers are used to remove layers of concrete/asphalt from existing roadways in preparation for paving operations. On the other hand, reclaimer/stabilizer machines prepare new surface material from an existing road bed by the pulverization of the road bed material. Such a machine includes a rotating cutter assembly confined within a cutter housing. The cutter housing may include a series of nozzle ports extending across the width of the housing which cooperate with spray nozzles to permit spraying of liquid additives into the cutter housing to be mixed with the salvaged material being pulverized, in order to provide the desired stabilized road bed. Alternatively, new road surfacing materials and/or liquid additives may be placed in front of the leading edge of the reclaimer/stabilizer during operation to be then mixed with the reclaimed surface material.
It is advantageous that the surface left behind by cold planer machines be of a reasonably uniform texture in nature, especially if traffic will be driven over the surface before it can be repaved. However, for many road surface repair/replacement operations, it is necessary to remove a portion of the road surface, such as the damaged portion and sections of the surface surrounding that damaged portion, to score the exposed surface so that the concrete or asphalt to be laid will more readily adhere to the exposed surface. For example, in a typical asphalt highway, the asphalt itself may have a depth of 3 to 10 inches. During renovation, it is not uncommon for up to, for example, 1 to 4 inches of the overall highway depth may be removed by the cold planer machines, with the remaining surface being scored to a depth of about 1/16 inches to about 3/16 inches. While it is desirable for such scored surfaces to be uniform in depth and pattern, non-uniform surfaces, such as wavy or grooved patterns on such surface, may arise if the ground speed of the portable machine chassis increases or decreases without making a proper adjustment in the rotational speed of the cutting drum. Thus, if ground speed is increased without increasing the speed of the cutter drum, the drum will make fewer rotations over a given linear distance, resulting in a non-uniform, wavy, grooved pattern, or even rougher road surface. Similarly, if the ground speed is decreased, without decreasing the rotational speed of the cutter drum, the drum will make greater rotations over a given linear distance, resulting in non-uniform, wavy or even rougher road surfaces. Moreover, certain states require that a consistent pattern be left by a cold planer and have requirements for gradation and blending of materials for reclaimer/stabilizer machines. Thus, changes in ground speed without the appropriate change in rotational speed of the cutter drum could alter the overall scored pattern and could alter the gradation and affect the blending characteristics of the reclaimed/stabilized material.
The need to provide a control of the cutter drum speed in relation to the travel of the machine can be seen when one considers the following. Assume a cylindrical cutter drum has a diameter of, for example, 46 inches and a length of 84 inches. Typically, rows of teeth are spread at a regular pattern on the cutter surface, such as, for example, 3 rows of teeth spaced about 48 inches circumferentially apart (which is equivalent to a spacing angle of about 120 degrees) for the drum described. The rows may have, for example, 135 individual teeth spaced a uniform linear distance apart, such as, for example ⅝ inches and at an equal projecting angle. If such a cutter operates at about 100 rpm's, each individual row of teeth will be in a position to contact the asphalt road surface about every 0.5 to 0.6 seconds. With three separate rows of teeth on the cutter drum, this means that a new row will make contact with the road surface about every 0.2 seconds. If the machine is moving at 60 feet per minute (or 1 foot per second), then each individual row of teeth will contact the road surface about every 0.6 feet. With three separate rows of teeth on the cutter drum, this means that a new row will contact the road surface about every 0.2 feet. However, if the ground speed were to change to about 90 feet per minute (about 1.5 feet per second), then each individual row of teeth will contact the pavement about every 0.9 feet. And with three separate rows of teeth on the cutter drum, this means a new row will now contact the pavement every 0.3 feet. This type of change in speed leads to an irregular, non-uniform tooth pattern, which causes a road to be rougher for automobiles that travel over the surface before it is resurfaced. Indeed, this type of speed change may lead to an undesirable wavy texture/tooth pattern in the surface that could cause vehicles that are traveling over the surface to veer toward one side of the road or the other; motorcycles are particularly prone to veer or deflect from the desired path of travel when encountering such a wavy texture.
Prior cold planer and reclaimer/stabilizer machines have previously enabled operators to provide a method of changing the cutter drum speed through the use of a multi-speed select transmission or through the process of removal and installation of sheaves of different diameters that are connected to the engine output and/or the cutter drum gearbox. However, these methods of changing drum speed are unsatisfactory. In the latter case (using sheave replacement), the work vehicle must be stopped in order to change the sheave, which is a time and labor intensive project. Even in vehicles where a multi-speed select transmission is used, the work vehicle still must remain in a very narrow speed range, or stopped altogether because the cutter drum speed cannot be changed “on the fly” with respect to the ground speed of the vehicle. Moreover, such multi-speed select transmissions typically do not contain sufficient gearing ratios to accommodate all conditions. Because changing cutter drum speed is so difficult in present cold planer and reclaimer/stabilizer machines, these machines oftentimes run at less than optimal conditions, i.e., do not operate at the proper ratio of ground speed to cutter drum speed, particularly in conditions where the work area is not flat, where the ground speed can easily vary from the speed at which the ratio is optimal. Non-optimum running conditions may also occur if the machine operator changes vehicle speed himself or where the road surface itself is such as to result in a cutting depth change.
Accordingly, there is a need for a system that will enable a machine, such as a cold planer or reclaimer/stabilizer machine, to better maintain the proper ratio of ground speed to cutter drum rotation during operation. Other needs will become apparent upon a reading of the following description, taken in conjunction with the drawings.